This invention relates to analog-to-digital converters, and more particularly, to analog-to-digital converters which are capable of being integrated as a semiconductor circuit.
Dual slope analog-to-digital converters divide the modes within a conversion sequence into three equal time periods of magnitude equal to the time required to count through all the states of a digital counter. The first time period is devoted to zeroing the system; the second time period is devoted to integration with the analog voltage, representing the measured parameter, switched into the circuit; and, the third time period devoted to integration with the analog reference voltage, representing full scale of the measured parameter, switched into the circuit. Conventionally, during the first time period, the storage element; ie, a capacitor, is discharged to 0 volts; during the second and third time periods, the measured parameter voltage is compared to the full scale reference voltage and the results latched in digital form which may be stored, displayed and/or utilized for some other desired purpose.
Conventional analog-to-digital converters of this type are implemented utilizing two or more separate integrated circuits and several external components. In addition, two or three power supply voltages are generally required for operation; e.g., +5 volts, +15 volts and -15 volts.
It is therefore an object of the present invention to provide an improved analog-to-digital converter.
Another object of the invention is to provide an analog-to-digital converter which is capable of being integrated on a single semiconductor substrate with few external components.
A further object of the invention is to provide an analog-to-digital converter which operates from a single relatively low-voltage, low-power supply.
It is another object of the invention to provide an analog-to-digital converter which is capable of being integrated as a semiconductor circuit utilizing I.sup.2 L techniques.
Still a further object of the invention is to provide an analog-to-digital converter which is integratable on a single substrate with digital circuitry to provide a complete analog and digital system on a single semiconductor chip.
Yet another object of the invention is to provide an analog input stage for a portable, battery-operable digital thermometer.